It is known that older people are more sensitive to cancer and infectious agents and need more time to recover from such disorders. Can this difference of sensitivity to cancer and infections between elderly and younger people be due to a difference in their immune systems and, more specifically, in the way monocytes (nonspecific immune system) react to infectious agents and cancer cells? What happens when the cells have aged remains to be determined. Our purpose is to compare in young and aged monocytes the processes of monocyte activation.